Stars argue the threat against WikiLeaks represents "a step into the darkness".

WikiLeaks founder Julian Assange prepares to speak from the balcony of the Ecuadorian embassy where he continues to seek asylum following an extradition request from Sweden in 2012Carl Court/Getty Images

Hundreds of journalists, human rights activists, retired military personnel and lawyers have signed an open letter that urges US president Donald Trump to "immediately close" any probe into both Julian Assange and his whistleblowing platform WikiLeaks.

"We call on you as President of the United States to close the Grand Jury investigation into WikiLeaks and drop any charges planned against any member of WikiLeaks," the letter reads, signed by well-known figures including Edward Snowden, Daniel Ellsberg and Noam Chomsky.

It emerged last month that CIA director Mike Pompeo, despite previously lauding WikiLeaks publications, had called the platform a "hostile intelligence service".

Attorney General Jeff Sessions claimed that arresting Assange had become a "priority".

Now, standing up to the US political establishment, other signatures on the open letter in defence of Assange include filmmakers Ken Loach and Oliver Stone, journalist John Pilger, musician PJ Harvey, actress Pamela Anderson and former NSA technician Bill Binney.

It states: "We are journalists, activists and citizens from the United States and around the world who care about press freedom and are writing to you in response to the latest threat of prosecution against WikiLeaks for its journalistic work.

"It is reported that charges, including conspiracy, theft of government property and violating the Espionage Act are being considered against members of WikiLeaks, and that charging WikiLeaks editor, Julian Assange, is now a priority of the Department of Justice (DoJ).

"A threat to WikiLeaks' work — which is publishing information protected under the First Amendment — is a threat to all free journalism. If the DoJ is able to convict a publisher for its journalistic work, all free journalism can be criminalised."

It concluded: "The kind of threat now facing WikiLeaks [...] is a step into the darkness."

The US intelligence community stepped up its anti-WikiLeaks rhetoric after the platform released tens of thousands of emails from US Democratic Party groups and politicians. Donald Trump, during the campaign trail, declared his love for the website.

Assange remains in the Ecuadorian embassy in London, where he has lived under political asylum since 2012. UK authorities have long said if he leaves the building he will be arrested and extradited to Sweden where he faces an allegation of rape, which he denies.

Most recently, WikiLeaks released a series of publications under the name 'Vault 7'. The leaks reportedly come from inside the US Central Intelligence Agency (CIA) and detail a number of so-called "cyberweapons" used to hack into electronic devices.